Shank adaptor for a rock drill



FIG. 1 is a reduced perspective view of a shank adaptor for a rock drill showing our new design;

FIG. 2 is a top end elevational view thereof;

FIG. 3 is a bottom end elevational view thereof;

FIG. 4 is a side elevational view thereof. 

The ornamental design for a shank adaptor for a rock drill, as shown and described. 